Moderator structures for nuclear reactors including a unitary header tank



Aprll 19, 1966 R. s. CHALLENDER ETAL 3,247,070

MODERATOR STRUCTURES FOR NUCLEAR REACTORS INCLUDING A UNITARY HEADER TANK Orlglnal Flled June 24, 1958 5 Sheets-Sheet l April 19, 1966 R. .CHALLENDER ETAL 3,247,070

FOR NUCLEAR MODERATO CTUR REACTORS INCLUD A U ARY HEADER TANK Orlginal Filed June 24, 1958 5 Sheets-Sheet 2 April lg, 1966 R. s. CHALLENDER ETAL 3,247,070

MODERATOR STRUCTURES FOR NUCLEAR REACTORS INCLUDNG A UNITARY HEADER TANK Original Filed June 24, 1958 5 Sheets-Sheet 3 United States Patent Ofi 3,247,070 Patented Apr. 19, 1956 ice MGDERATOR STRUCTURES FR NUCLEAR RE- ACTRS lNCLUDING A UNITARY HEADER TANK Ronald Scott Challender, Appleton, near Warrington, and Dennis Ross'Poulter, Cuicheth, Warrington, England, assignors to United Kingdom Atomic Energy Authority, London, England Continuation of application Ser. No. 744,207, June 24,

1958. This appiication Jan. 10, 1963, Ser. No. 250,597 Claims priority, application Great Britain, June 24, 1957, 19,896/57 3 Claims. (Cl. 176-30) The present application for patent -is a continuation of patent application Serial No. 744,207, filed June 24 ,1958, now abandoned.

This invention relates to nuclear reactors and it has an applic-ation in the sodiumdgna-phite reactor disclosed in detail in a co-pending application Seri-al No. 744,185, now issued as U.S. Letters Patent No. 3,000,728, of even date filed in the names of Everett Long and Ronald Scott Challender and of common assignee.

According to the present invention a moderator structure for a nuclear reactor comprises vertical columns of graphite blocks spaced to provide vertical passageways Ithrough the structure, the columns having means providing for their location independent of one ano-ther and mea-ns defining coolant channels passing lengthwise through the columns.

The structure of the invention allows for thermal and irradiation growth of the columns in Iall directions without creating undue stressing of the structure; it also allows free growth at one end (norm-ally the hot end) in excess of that at the other end (normally the cold end); it also allows for the graphite structure to be cooled :by a coolant passed through the pasageways, the heat extracted being usefully employed, whilst providing that the lower neutron energy level consequent upon the lolWer moderator ,temperature improves the nuclear properties .of the reactor in the course of its operation. Problems of differential thermal expansion as between the graphite and other materials (such as steel supports) are avoided or substantially reduced.

The above structure is particularly useful in a re-entrant cooled design of sodium-graphite reactor where the outer (or thimble) tube of the Ire-entrant system is supported at the lower end of the graphite structure and is readily located with `feed tubes at the top of the reactor. A space is left between the thimble tube and the moderator structure so that further cooling of the moderator can take place.

One embodiment of the invention will now be described by way of example with reference to the accompanying drawing in which:

FIG. 1 is a Vertical sectional elevation of a moderator structure.

FEG. 2 is a sectional plan along the line II-II of FIG. 1.

FIG. 3 is a sectional plan along the line III-III of FIG. 1.

FIG. 4 is an enlarged detail of a neutron shield forming part of the structure of FIG. l.

FIG. 5 is a schematic sectional elevation of a moderator structure fitted with a re-entrant cooling system.

FIG. 6 is an enlarged detail of the lower part of FIG. 5.

In' FIG. 1 there is shown in general outline a moderator structure 1 comprising a core region 2 and upper and lower reflector regions 3 and 4 surmounted by an upper neutron shield 5. The upper and lower reilector regions 3 and 4 each comprises a layer of spaced hexagonal cross-section graphite blocks 6, the blocks 6 of the lower reflector region 4 resting on a perforated core plate 7. The core region 2 comprises a further five layers of graphite bricks 6 and the neutron shield 5 comprises regions 3 and 4 each comprises a layer of spaced hexagonal cross-section. The blocks 6 form vertical columns 9 and are formed to define vertical channels 1t) passing through the structure 1. The columns of blocks 6 forming the structure 1 are spigotted together, spigots 11 formed on the blocks 6 of any `layer engaging with spigot holes 12 in the blocks 6 of lower adjacent layers, excepting two central layers 13 and 14 of blocks 6 which are separated by a layer of spaced hexagonal tiles 15 having spigots 16 and spigot holes 17 respectively similar to the spigots 11 and the spigot holes 12 of the blocks 6. The spigots 11 of the blocks 6 forming the lower reflector region 4 engage with spigot holes 18 formed in the core plate 7. The tiles -15 are formed to preserve the continuity of the channels 10 and have three equally spaced internal projections 19.

As shown in FIG. 2 the blocks 6 of the core region 2 and the upper :and lower reflector 4regions 3 and 4 are spaced apart face to face thus defining vertical passageways 20 through the structure 1. The core plate 7 has drillings 22 connecting with the passageways 20.

Referring -to FIGS. 3 and 4 in conjunction with FIG. 1, the neutron shield 5 is formed from composite steel canned graphite bricks 8. The bricks `8 comprise a hexagonal mild steel can 23 containing three sections of graphite 24 separated by boron steel shims 25. The can 23 is closed top and bottom by boron .steel end plates 26. The neutron shield 5 is built up from three layers of the bricks 8, each layer being staggered in relationship to lower layers. The bricks 8 are formed to define eX- tensions 27 of the channels 10 but of smaller diameter. The bricks 8 have sho-rt spigot-s 28 engaging with spigot holes 29 in the bricks 8 of' yadjacent lower layers while the spigots 28 of the bottom layer of bricks 8 engage with the spigot holes 12 in the bricks 6 of the upper reflector region 3. Each of the bricks S has two diametrically opposed internal longitudinal chases 30- and the radial position off the chases 30 is staggered by 60 in consecutive layers of the bricks 8 to obviate vertical gaps in the neutron shield 5. As shown in FIGS. 3 and 4 the bricks 8 are spaced apart face to face thus defining, with cut away parts 3'1 of the bricks 8, 4a staggered passageway 32 through the neutron shield 5 connecting with the passageways 20'. The bricks 6 are additionally coupled together by pegs 33.

As shown in FIG. 5 each column 9 of graphite blocks (6 and 8) is located by spigot tubes 34 projecting from a sodium header tank 35 and by the core plate 7. The spigot tubes 34 define lower lfuel servicing apertures 46 in the tank 35. The tank 35 also has fuel servicing stand pipes 47 defining upper fuel servicing apertures 48, each aperture being in line with one of the channels 10 and one of the apertures 46. FIG. 5 shows zirconium thimble tubes 36 forming part of a re-entrant cooling system -in which liquid sodium is passed from the sodium header tank 35 through annular spaces between the zirconium tubes 36 and concentric inner tubes (not shown) and thence through the inner tubes over fuel elements contained. The zirconium tubes 36 have a lower closed end 37 and pass through the channels 10 and their extensions 27. The zirconium tubes 36 are sealed at their upper ends 38 in the spigot tubes 34 and .are located at their lower closed ends by pegs 39 engaging with spiders 40 carried by the core plate 7 within drillings 21. The tubes 36 are intermediately located in the channels 10 by the projections 19 of the tiles 15.

Referring to FIG. 6 there is shown part of the core plate 7 and one of the spiders 40 comprising a cylindrical body 41 fitted into one drilling 2l of the core plate 7 with a central boss 42 located by three integral spider legs 43. The peg 39 which is screwed into the closed end 37 of the zirconium tube 36 is fitted with a flow restrietor 44 in the form of a tapered ring. In operation of the reactor, gaseous coolant for the graphite (as indicated by the arrows 45 in FIG. 5) is fed through the drillings 2.1 in the core plate 7, through the annular spaces between the walls of the channels 10 and the zirconium tubes 36, through the chases 30 and thence out through the spigot tubes 34. Gas'eous coolant is also fed through the passageways 20 `and thence out of the structure 1 .through the staggered passageways 32 in the neutron shield 5.

The direction of minimum Wigner growth of the graphite in the graphite blocks 6 is arranged longitudinally thereof and the passageways 20 and 32 are made of sufcient width to accommodate lateral Wigner growth Whilst still allowing the passage of a coolant.

Differential thermal movements between the sodium tank 3S and the core plate 7 is accommodated by tilting of the columns 9 which can be tolerated. The spigot tubes 34 provide that alignment is maintained between each of the channels 10 and its associated pair of apertures 46, 48 for fuel servicing purposes (fuel servicing being fully described in the above-mentioned co-pending application Serial No. 744,185 now U.S. Patent No. 3,000,728).

We claim:

l. A nuclear reactor moderator structure comprising a plurality of upright graphite columns, said columns dening channels for .fuel elements and coolant, the channels extending in the direction of the columns, a base plate disposed `below said columns, a unitary header tank disposed above said columns and defining fuel element servicing apertures, means keying the lower end of each column to said base plate, and spigot tube connections between said tank and said channels at the upper ends of the columns, each connection aligning one of said apertures with lone of said channels.

2. A nuclear reactor moderator structure comprising a, plurality of upright graphite columns, said columns' defining channels lfor fuel elements and coolant, saidchannels extend-ing in the direction of the columns, a base plate disposed below said columns, a unitary header tank disposed above said columns, said tank having fuel servicing apertures, means keying the lower end of each column to said base plate, and spigot tube connections between said tank and said channels at the upper ends of the columns, each connection comprising a spigot tube disposed around one of the apertures and projecting downwardly to engage the upper end of one of the columns thereby aligning said one of the apertures lwith one of said channels.

3. A nuclear reactor moderator structure comprising a plurality of upright columns of graphite blocks, said columns defining channels for fuel elements and coolant, said channels extending in the direction of the columns, a base plate disposed transversely of the direction of and below said columns, iinst means keying the lower-most block of each of the columns to said base plate, second means keying the blocks of each column to adjacent blocks in said column, a unitary header tank disposed transverselyof .the direction of and above said columns, said tank having pairs of aligned fuel servici-ng apertures, each pair being associated with one of said channels, and spigot tube connections between the tank and the channels in the uppermost blocks of the columns, each connection comprising a spigot tube disposed round the lower-most one of each pair of aligned fuel servicing apertures and aligning that pair with its associated channel, and said first and second means and spigot tube connections serving to space said columns apart to detine moderator coolant passageways extending in the direction of the columns.

References Cited by the Examiner UNITED STATES PATENTS 8/1959 Schultz -176-78 11/1961 Battle 176-84 OTHER REFERENCES Y REUBEN EPSTEIN, Primary Examiner.

CARL D. QUARFORTH, Examiner. 

1. A NUCLEAR REACTOR MODERATOR STRUCTURE COMPRISING A PLURALITY OF UPRIGHT GRAPHITE COLUMNS, SAID COLUMNS DEFINING CHANNELS FOR FUEL ELEMENTS AND COOLANT, THE CHANNELS EXTENDING IN THE DIRECTION OF THE COLUMNS, A BASE PLATE DISPOSED BELOW SAID COLUMNS, A UNITARY HEADER TANK DISPOSED ABOVE SAID COLUMNS AND DEFINING FUEL ELEMENT SERVICING APERTURES, MEANS KEYING THE LOWER END OF EACH COLUMN TO SAID BASE PLATE, AND SPIGOT TUBE CONNECTIONS BETWEEN SAID TANK AND SAID CHANNELS AT THE UPPER ENDS OF THE COLUMNS, EACH CONNECTION ALIGNING ONE OF SAID APERTURES WITH ONE OF SAID CHANNELS. 